Integrated Services Digital Network (I.S.D.N) is an international communications standard that makes it possible to deliver multiple services in addition to the normal telephone (voice) service and change consequently, fax, video, data and all kinds of images can be transmitted to a terminal over a single line. The ISDN is provided by public network operators at both national and international levels which offer a choice of Basic or Primary Rate access to the ISDN network. The basic access (also called 2B+D) provides two 64 kbps channels for voice or data communications plus one extra D channel for the controlling and the monitoring of the transmission, giving an aggregate speed of 144 Kbps. The primary rate (which is called 30B+D) offers up to 30 simultaneous 64 Kbps B-channels and one 64 kbps D channel for an aggregate speed of 2,048 Kbps (referred to as E1) or 23 simultaneous 64 Kbps B channels and one 64 Kbps D channel for an aggregate speed of 1,53 Kbps in the case of a T1 primary channel.
The performances offered by the ISDN networks, and particularly the speed provided by the primary rate will allow the development of powerful and effective multimedia applications in which data, images and voice will be processed. However, in order to ensure that a maximum number of different software applications take advantage of the substantial performances of the ISDN networks, it is highly desirable that multiple different telecommunication links having a wide range of different speeds be provided.
European patent application Number 91480136.0 entitled "Apparatus for connecting a communicating equipment to a digital communication network having at least two digital communication channels" filed on Aug. 29th 1991, not published at the date of filing of the present patent application and assigned to the assignee of the present application discloses an apparatus providing the aggregation of two B-channels in order to provide a single 144 kbps channel which is fully transparent to the application. However, in this system it remains necessary to measure the delay which exists between the different channels forming the required aggregate channel. Therefore, in view of the different possible requirements which are likely to exist, it is highly desirable to provide the aggregation of a subset of the 30 B-channel existing in the ISDN primary frame in order to provide one link having a predetermined speed of 64 Kbps, 128 Kbps, 192 Kbps, etc . . . In addition, it is desirable to provide a fractional T1 or multi-channel E1 (according to I431 CCITT recommendations) at a rate of nx64 Kbps, with n being equal to 1, 2, 3, 4, etc . . .